The quickest way to correct MBD is to take the chameleon to a vet to get shots of calcium and when the blood calcium levels are high enough to give it an injection of calcitonin to quickly draw the calcium back into the bones.
The next best option from my experience is to give it liquid calcium sandoz or gluconate.
Once you have the calcium levels back in balance its important to keep them there through good husbandry....proper supplements, lighting, temperatures and insect care.
Exposure to UVB light allows the chameleon to produce D3 so that it can use the calcium in its system. Appropriate temperatures aid in digestion and thus indirectly in nutrient absorption.
Dusting with calcium at most feedings helps to make up for the usually poor ratio of calcium to phos founding most of the feeder insects.
Supplementing twice a month with the vitamin powder that contains a beta carotene (prOformed) source of vitamin A will ensure that it gets its vitamins without overdosing the vitamin A. It leaves the owner in control of the prEformed vitamin A. PrOformed sources will not build up in the system like prEformed vitamin A will.
Dusting with a calcium/D3 powder twice a month ensures that the chameleon gets some D3 without overdosing it and leaving it to produce the rest from its exposure to the UVB.
Feeding/gutloading the insects well also helps.